The present invention relates generally to equipment for processing semiconductor wafers. More particularly, the present invention relates to an air platen used to support a linear belt during the chemical mechanical polishing of semiconductor wafers.
Chemical mechanical polishing (CMP) is used for planarizing semiconductor wafers during processing of the wafers. Because semiconductor circuits on wafers are commonly constructed in layers, where a portion of a circuit is created on a first layer and conductive vias connect it to a portion of the circuit on the next layer, each layer can add or create topography on the wafer that must be smoothed out before generating the next layer. In order to improve the manufacturability of the circuits on the wafer, many processing steps require planarizing the wafer surface. For example, to improve the uniformity of deposition of the conductive vias, the wafer is planarized prior to deposition to reduce the peaks and valleys on the surface over which the metal is deposited.
In conventional planarization technology, a rotating wafer carrier head brings the wafer into contact with a polishing pad rotating in the plane of the wafer surface to be planarized, and pressure is applied to a semiconductor wafer in order to support the wafer face down against a moving polishing pad. One type of polishing or planarizing apparatus is the linear polisher. In linear planarizing technology, an endless belt travels over two or more rollers. The wafer is placed against the moving polishing surface of the belt. An example of a linear polishing system is the Teres™ CMP System manufactured by Lam Research Corporation, Fremont, Calif.
A key component of a linear CMP system is the air platen. The air platen provides a cushion of air via air channels to support the belt as pressure is applied to the wafer. However, existing air platen may not provide a cushion of air that takes into account variations in the wafer surface when it is placed against the belt surface, leading to a wafer that is not uniformly polished. If this occurs, there may be topography that is not removed from the wafer surface, or else the wafer surface may be planarized to the point where pitting will occur on the wafer surface.
Another problem that is associated with air platen is that the portions of the belt that support the edge of the wafer often themselves are not properly supported by the air platen. This may result in what is known as edge exclusion. Edge exclusion categorically is a portion of the wafer edge that does not receive the same degree of polishing action as the balance of the wafer. The result is a reduction of usable area for product production.
Accordingly, there is a need in the art for an improved air platen for CMP systems.